diff --git a/src/libstl/stla_read.c b/src/libstl/stla_read.c
index 9ef095b..a1d58ed 100644
--- a/src/libstl/stla_read.c
+++ b/src/libstl/stla_read.c
@@ -429,7 +429,7 @@ static void parse_xyz_coords(foug_stla_parse_data_t* data, foug_stl_coords_t* co
   } /* end switch */
 }
 
-static void parse_facets(foug_stla_parse_data_t* data)
+static void parse_facets(foug_stla_parse_data_t* data, size_t i_facet_offset)
 {
   if (!parsing_can_continue(data))
     return;
@@ -458,12 +458,13 @@ static void parse_facets(foug_stla_parse_data_t* data)
     parsing_eat_token(ENDFACET_token, data);
 
     if (parsing_can_continue(data)
-        && data->geom != NULL && data->geom->process_next_triangle_func != NULL)
+        && data->geom != NULL
+        && data->geom->process_triangle_func != NULL)
     {
-      data->geom->process_next_triangle_func(data->geom, &facet);
+      data->geom->process_triangle_func(data->geom, &facet, i_facet_offset);
     }
 
-    parse_facets(data);
+    parse_facets(data, i_facet_offset + 1);
     break;
   }
   default:
@@ -479,7 +480,7 @@ static void parse_solid(foug_stla_parse_data_t* data)
   switch (data->token) {
   case SOLID_token:
     parse_beginsolid(data);
-    parse_facets(data);
+    parse_facets(data, 0);
     parse_endsolid(data);
     break;
   default:
diff --git a/src/libstl/stla_read.h b/src/libstl/stla_read.h
index 4aa36f0..26528e7 100644
--- a/src/libstl/stla_read.h
+++ b/src/libstl/stla_read.h
@@ -11,7 +11,7 @@ struct foug_stla_geom_input
 {
   void* cookie;
   void (*begin_solid_func)          (foug_stla_geom_input_t*, const char*); /* Optional */
-  void (*process_next_triangle_func)(foug_stla_geom_input_t*, const foug_stl_triangle_t*);
+  void (*process_triangle_func)(foug_stla_geom_input_t*, const foug_stl_triangle_t*, uint32_t);
   void (*end_solid_func)            (foug_stla_geom_input_t*, const char*); /* Optional */
 };
 
diff --git a/src/libstl/stla_write.c b/src/libstl/stla_write.c
index d7daeb1..22920de 100644
--- a/src/libstl/stla_write.c
+++ b/src/libstl/stla_write.c
@@ -109,7 +109,7 @@ int foug_stla_write(foug_stla_geom_output_t* geom,
                     foug_transfer_t* trsf,
                     uint8_t real32_prec)
 {
-  size_t solid_count = 0;
+  const size_t solid_count = geom != NULL ? geom->solid_count : 0;
   size_t total_facet_count = 0;
   size_t written_facet_count = 0;
   size_t isolid = 0;
@@ -139,12 +139,6 @@ int foug_stla_write(foug_stla_geom_output_t* geom,
     /* TODO: check the "format" string can contain the given precision */
   }
 
-  /* Get solid count */
-  if (geom->get_solid_count_func != NULL)
-    solid_count = geom->get_solid_count_func(geom);
-  else
-    solid_count = 1;
-
   /* Compute total facet count */
   if (trsf->task_control.handle_progress_func != NULL) {
     for (isolid = 0; isolid < solid_count; ++isolid)
diff --git a/src/libstl/stla_write.h b/src/libstl/stla_write.h
index 739afce..5bec359 100644
--- a/src/libstl/stla_write.h
+++ b/src/libstl/stla_write.h
@@ -11,10 +11,10 @@ struct foug_stla_geom_output
 {
   void*  cookie;
 
-  size_t (*get_solid_count_func)   (foug_stla_geom_output_t*); /* Optional (if NULL solid_count == 1) */
-  void   (*get_solid_name)         (foug_stla_geom_output_t*, size_t, char*); /* Optional */
-  size_t (*get_triangle_count_func)(foug_stla_geom_output_t*, size_t);
-  void   (*get_triangle_func)      (foug_stla_geom_output_t*, size_t, size_t, foug_stl_triangle_t*);
+  size_t solid_count;
+  void   (*get_solid_name)         (const foug_stla_geom_output_t*, size_t, char*); /* Optional */
+  size_t (*get_triangle_count_func)(const foug_stla_geom_output_t*, size_t);
+  void   (*get_triangle_func)      (const foug_stla_geom_output_t*, size_t, size_t, foug_stl_triangle_t*);
 };
 
 /* Write geometry in the STL ascii format */
diff --git a/src/libstl/stlb_read.c b/src/libstl/stlb_read.c
index fc1cf5d..f37a106 100644
--- a/src/libstl/stlb_read.c
+++ b/src/libstl/stlb_read.c
@@ -28,13 +28,14 @@ static void read_triangle_alignsafe(const uint8_t* buffer, foug_stlb_triangle_t*
 
 static void foug_stlb_read_facets(foug_stlb_geom_input_t* geom,
                                   uint8_t* buffer,
-                                  uint32_t facet_count)
+                                  uint32_t facet_count,
+                                  uint32_t i_facet_offset)
 {
   foug_stlb_triangle_t triangle;
   uint32_t buffer_offset;
   uint32_t i_facet;
 
-  if (geom == NULL || geom->process_next_triangle_func == NULL)
+  if (geom == NULL || geom->process_triangle_func == NULL)
     return;
 
   buffer_offset = 0;
@@ -48,7 +49,7 @@ static void foug_stlb_read_facets(foug_stlb_geom_input_t* geom,
     buffer_offset += FOUG_STLB_TRIANGLE_RAWSIZE;
 
     /* Declare triangle */
-    geom->process_next_triangle_func(geom, &triangle);
+    geom->process_triangle_func(geom, &triangle, i_facet_offset + i_facet);
   }
 }
 
@@ -105,7 +106,7 @@ int foug_stlb_read(foug_stlb_geom_input_t* geom,
     if (foug_datax_no_error(error)) {
       uint8_t progress_pc;
 
-      foug_stlb_read_facets(geom, trsf->buffer, facet_count_read);
+      foug_stlb_read_facets(geom, trsf->buffer, facet_count_read, accum_facet_count_read);
       accum_facet_count_read += facet_count_read;
       progress_pc = foug_percentage(0, total_facet_count, accum_facet_count_read);
       if (!foug_task_control_handle_progress(&trsf->task_control, progress_pc))
diff --git a/src/libstl/stlb_read.h b/src/libstl/stlb_read.h
index 1b63f67..36d5f76 100644
--- a/src/libstl/stlb_read.h
+++ b/src/libstl/stlb_read.h
@@ -11,10 +11,10 @@ typedef struct foug_stlb_geom_input foug_stlb_geom_input_t;
 struct foug_stlb_geom_input
 {
   void* cookie;
-  void  (*process_header_func)       (foug_stlb_geom_input_t*, const uint8_t*); /* Optional */
-  void  (*begin_triangles_func)      (foug_stlb_geom_input_t*, uint32_t);       /* Optional */
-  void  (*process_next_triangle_func)(foug_stlb_geom_input_t*, const foug_stlb_triangle_t*);
-  void  (*end_triangles_func)        (foug_stlb_geom_input_t*);                 /* Optional */
+  void  (*process_header_func)  (foug_stlb_geom_input_t*, const uint8_t*); /* Optional */
+  void  (*begin_triangles_func) (foug_stlb_geom_input_t*, uint32_t);       /* Optional */
+  void  (*process_triangle_func)(foug_stlb_geom_input_t*, const foug_stlb_triangle_t*, uint32_t);
+  void  (*end_triangles_func)   (foug_stlb_geom_input_t*);                 /* Optional */
 };
 
 /* foug_stlb_read() */
diff --git a/src/libstl/stlb_write.c b/src/libstl/stlb_write.c
index f4ef18e..7fe9dbf 100644
--- a/src/libstl/stlb_write.c
+++ b/src/libstl/stlb_write.c
@@ -53,7 +53,7 @@ int foug_stlb_write(const foug_stlb_geom_output_t* geom,
                     foug_transfer_t* trsf,
                     foug_endianness_t byte_order)
 {
-  uint32_t facet_count;
+  const uint32_t facet_count = geom != NULL ? geom->triangle_count : 0;
   uint32_t i_facet;
   uint32_t buffer_facet_count;
   uint32_t ifacet_start;
@@ -63,8 +63,6 @@ int foug_stlb_write(const foug_stlb_geom_output_t* geom,
     return FOUG_DATAX_NULL_BUFFER_ERROR;
   if (trsf->buffer_size < FOUG_STLB_MIN_CONTENTS_SIZE)
     return FOUG_DATAX_INVALID_BUFFER_SIZE_ERROR;
-  if (geom == NULL || geom->get_triangle_count_func == NULL)
-    return FOUG_STLB_WRITE_NULL_GET_TRIANGLE_COUNT_FUNC;
   if (geom == NULL || geom->get_triangle_func == NULL)
     return FOUG_STLB_WRITE_NULL_GET_TRIANGLE_FUNC;
   if (byte_order != FOUG_LITTLE_ENDIAN/* && byte_order != FOUG_BIG_ENDIAN*/)
@@ -72,18 +70,20 @@ int foug_stlb_write(const foug_stlb_geom_output_t* geom,
 
   /* Write header */
   {
-    uint8_t header_data[FOUG_STLB_HEADER_SIZE];
-    if (geom->get_header_func != NULL)
-      geom->get_header_func(geom, header_data);
-    else
-      memset(header_data, 0, FOUG_STLB_HEADER_SIZE);
-
+    const uint8_t* header_data = NULL;
+    if (geom->header != NULL) {
+      header_data = geom->header;
+    }
+    else {
+      /* Use buffer to store an empty header (filled with zeroes) */
+      memset(trsf->buffer, 0, FOUG_STLB_HEADER_SIZE);
+      header_data = (const uint8_t*)trsf->buffer;
+    }
     if (foug_stream_write(&trsf->stream, header_data, FOUG_STLB_HEADER_SIZE, 1) != 1)
       return FOUG_DATAX_STREAM_ERROR;
   }
 
   /* Write facet count */
-  facet_count = geom->get_triangle_count_func(geom);
   if (byte_order == FOUG_LITTLE_ENDIAN)
     foug_encode_uint32_le(facet_count, trsf->buffer);
   else
diff --git a/src/libstl/stlb_write.h b/src/libstl/stlb_write.h
index 7db3dbb..27f35f2 100644
--- a/src/libstl/stlb_write.h
+++ b/src/libstl/stlb_write.h
@@ -11,9 +11,9 @@ typedef struct foug_stlb_geom_output foug_stlb_geom_output_t;
 struct foug_stlb_geom_output
 {
   void*    cookie;
-  void     (*get_header_func)        (const foug_stlb_geom_output_t*, uint8_t*); /* Optional */
-  uint32_t (*get_triangle_count_func)(const foug_stlb_geom_output_t*);
-  void     (*get_triangle_func)      (const foug_stlb_geom_output_t*, uint32_t, foug_stlb_triangle_t*);
+  uint8_t* header; /* May be NULL if empty header*/
+  uint32_t triangle_count;
+  void     (*get_triangle_func)(const foug_stlb_geom_output_t*, uint32_t, foug_stlb_triangle_t*);
 };
 
 /* foug_stlb_write() */
@@ -22,8 +22,7 @@ FOUG_DATAX_LIBSTL_EXPORT int foug_stlb_write(const foug_stlb_geom_output_t* geom
                                              foug_endianness_t              byte_order);
 
 /* Specific error codes returned by foug_stlb_write() */
-#define FOUG_STLB_WRITE_NULL_GET_TRIANGLE_COUNT_FUNC 1
-#define FOUG_STLB_WRITE_NULL_GET_TRIANGLE_FUNC       2
-#define FOUG_STLB_WRITE_UNSUPPORTED_BYTE_ORDER       3
+#define FOUG_STLB_WRITE_NULL_GET_TRIANGLE_FUNC       1
+#define FOUG_STLB_WRITE_UNSUPPORTED_BYTE_ORDER       2
 
 #endif /* FOUG_DATAX_C_LIBSTL_STLB_WRITE_H */